1. Field of the Invention
The present invention relates generally to spraying, and in particular to agricultural spraying with vehicle-mounted spraying equipment, and more particularly to agricultural spraying with independent control of spray droplet sizes and application rates, and with a position-responsive control system.
2. Description of the Related Art
Spraying is a well-known method of applying a wide variety of bulk materials, primarily in liquid and powdered form in a fluid propellant medium. Such spray materials can be dispensed in air currents, under liquid pressure, by gravity flow, or with any other suitable discharge means.
Spray application of bulk materials offers many potential advantages, including efficiency, uniformity of coverage and flexibility to adapt spraying equipment to various conditions unique to the objects being sprayed and their particular environments.
However, a disadvantage with many spray systems relates to the drift of spray particles and droplets away from their intended targets. Such drift is at best inefficient, as in the case of the overspray which represents wasted spray material, and in more serious situations can cause damage to nearby property, environment and people.
The field of agricultural spraying includes pesticide application for crop pest management and the application of fertilizer and growth regulators for nutrient management. The agricultural spraying industry is quite large, with pesticides alone currently accounting for approximately $3,000,000,000 in estimated annual expenditures. However, the use of pesticides in agricultural applications produces substantial benefits in crop yields with an estimated annual savings of approximately $12,000,000,000 in crops which would otherwise be lost to pests. The spray application of fertilizers and growth regulators likewise produces substantial benefits in crop yields and the like.
Notwithstanding the substantial advantages of agricultural spraying applications of pesticides and other spray materials, agricultural spraying is generally a relatively inefficient process. Factors which contribute to such inefficiencies include the susceptibility of sprayed materials to wind drift, overspray and inaccurate placement on the intended target crop plants. Irregularities in terrain and nonuniform plantings also contribute to the inconsistent and inefficient application of agricultural spray materials. Moreover, variations in ambient conditions such as wind, humidity levels and temperature tend to reduce the uniformity and efficiency with which spray materials are applied to their intended crop targets.
In addition to the inefficiencies associated with misdirected agricultural spray materials, overspray and spray drift can create significant problems if the materials are inadvertently applied to adjoining areas for which they were not intended. Such misapplication of agricultural spray materials can result in crop damage, injury to livestock, contamination of environmentally-sensitive areas and unnecessary human exposure to toxic materials.
The problems associated with the misapplication of agricultural spray materials are exacerbated by the use of larger spraying equipment covering wider swaths, high speed vehicles, air-blast spraying, and by aerial spraying. The inherent difficulties associated with large-scale spraying operations are balanced against the relative efficiencies which are achieved by covering larger areas more rapidly with wide-swath spraying equipment.
The Heiniger et al. U.S. Pat. No. 5,348,226 discloses a spray boom system with automatic boom end height control which uses an ultrasonic height control system for conforming the spray boom orientations to topography and slope of a zone being sprayed in order to increase uniformity of coverage. Uniform spray nozzle height can be a significant factor in achieving uniform spray material coverage.
Another important factor in spray material deposition control is the droplet size spectrum of the liquid being sprayed. Spray droplet size has been shown to significantly affect both the efficacy of pesticide treatments and the potential for off-target spray movement. Such off-target movement and deposition of spray is often called "spray drift". Insecticides, fungicides, growth regulators and post-emergence herbicides are generally more effective when applied using relatively small droplets, which tend to provide greater penetration of plant canopies and uniform coverage of foliar surfaces. Smaller spray droplets, with shorter mechanical relaxation times, have the advantage of more closely following air currents into dense plant canopies for achieving greater penetration and more uniform coverage. Conversely, such droplet mobility associated with smaller droplet sizes can exacerbate problems associated with spray drift away from application sites. Generally speaking, larger droplets tend to fall more directly due to their greater mass and are thus less susceptible to spray drift, evaporation, etc.
A common technique for controlling the-application rate of spray liquid involves adjusting the spray liquid pressure, for example, with the use of a throttling valve in a main distribution line of a spray liquid distribution system. However, altering the liquid pressure also generally alters the droplet size, thus effecting the deposition and its susceptibility to spray drift, evaporation, etc.
The Giles et al. U.S. Pat. No. 5,134,961 discloses an electrically actuated variable flow control system wherein solenoid valves are actuated by square wave pulses, which can be varied in frequency and duty cycle for controlling volumetric flow through spray nozzles. The volumetric flow rate can thus be varied without changing droplet size and spray pattern since the liquid supply pressure can be maintained constant. However, heretofore there has not been available a control system for a spray system which combines selective and independent control of the flow rate and the median droplet size setpoints with the advantages and features of the present invention.
In addition to the aforementioned advantages of independently and selectively controlling the application rate and median droplet size setpoints, substantial advantages can be achieved by controlling spray deposition with respect to field position of a spray vehicle, such as a ground vehicle or an aircraft. Such position-responsive control can be important because spray zones in and around a field to be sprayed can require different treatment by a spray system, ranging from little or no application of spray materials (i.e., outside the boundary of a given site) to a maximum application rate in heavily infested areas or regions of poor fertility. The boundaries for such differential application rate spray zones can be irregular, with such irregularities increasing the difficulty of manually altering spray system operating conditions by an on-board operator. Moreover, problems can arise due to operator reaction times when changed field conditions call for adjustments to the spray conditions. For example, if an operator is alerted that he or she has crossed a field boundary or property line and initiates a procedure for altering spray application, most spray control systems have an inherent delay which may cause overspray problems.
To address some of these problems, control systems and methodology have heretofore been developed which respond to spray vehicle positions. For example, the Ortlip U.S. Pat. No. 4,630,773 discloses a method and apparatus for spraying fertilizer wherein a computerized control system includes a field map with digital information concerning various soil types. The control system disclosed therein dispenses fertilizer in accordance with the optimum applications for the different soil conditions encountered in a target field. The spray liquid application rate is automatically adjusted for vehicle speed. Sensors are disclosed for determining malfunctions of the application hardware. However, the application control provided by the Ortlip apparatus occurs only along the direction of travel and not along the boom section. Moreover, the Ortlip apparatus does not provide for droplet size control, drift control or spray transport modeling for spray liquid deposition prediction.
Recent improvements in the accuracy and effectiveness of the global positioning system (GPS) for civilian applications have also created opportunities for greater automation of agricultural spraying by controlling agricultural spraying equipment with positioning systems responsive to specific field conditions. For example, the Teach U.S. Pat. No. 5,334,987 discloses an agricultural aircraft control system using the global positioning system. The Teach agricultural aircraft control system is adapted for automatically opening a dispenser valve for releasing chemicals in response to the aircraft flying within the boundaries of an agricultural field. Moreover, the Teach system provides for recording flight data. However, the Teach system does not provide for droplet size control, drift reduction, spray transport modeling and gradients of application rates to avoid drift in the combination of the present invention.
A similar system is available from Trimble Navigation, Sunnyvale, Calif. 94088-3642 under its trademark "TrimFlight GPS". Mother GPS-based agricultural spray control system is available from Satloc of Tempe, Ariz.
Models for predicting dispersion and deposition of aerially released material have been in development for approximately the past 25 years in joint projects between the U.S.D.A. Forest Service, in cooperation with the U.S. Army. Computerized codes which are currently available include AGDISP (Agricultural DISPersal) (Bilanin et al., 1989) and FSCBG (Forest Service Cramer-Barry-Graham) (Teske et al., 1992b). Such computerized models can be useful for predicting dispersion patterns of various liquids under a variety of ambient conditions, heights, etc.
The problems associated with overspray in agricultural spraying operations can be detected with instruments such as a detector for spray particles, which is available under the trademark "DRIFT SENTRY" from Custom Farm Services, Stanfield, Ariz. 85272. Such spray particle monitors can be placed at the perimeters of fields being sprayed and provide appropriate radio transmission warning signals, which can be received in an agricultural spray aircraft.